Mixed unsymmetric oxadiazoline and/or imine platinum(ii) complexes

Article abstract of DOI:10.1039/b704329e

Iminoacylation of acetone oxime Me₂CNOH 2 upon reaction with trans-[PtCl₂(NCCH₂CO₂Me)₂] 1 and [2 + 3] cycloaddition of acyclic nitrone ^-O⁺N(Me)C(H)(C ₆H₄Me-4) 3 to a nitrile ligand in 1 lead to the formation of mono-imine trans-[PtCl₂(imine-a)(NCCH₂CO ₂Me)] 4 [imine-a = NHC(CH₂CO₂Me)ONCMe ₂] and mono-oxadiazoline trans-[PtCl₂(oxadiazoline-a) (NCCH₂CO₂Me)] 6 [oxadiazoline-a = NC(CH₂CO ₂Me)ON(Me)C(H)(C₆H₄Me-4)] unsymmetric mixed ligand complexes, respectively, as the main products. Reactions of 6 or 4 with acetone oxime 2, cyclic nitrone ^-O⁺NCHCH ₂CH₂CMe₂ 8 or N,N-diethylhydroxylamine 11 give access, in moderate to good yields, to the unsymmetric mixed ligand oxadiazoline and/or imine complexes trans-[PtCl₂(oxadiazoline-a)(imine-a)] 9, trans-[PtCl₂(oxadiazoline-a)(oxadiazoline-b)] 10 [oxadiazoline-b = NC(CH₂CO₂Me)ONC(H)CH₂CH₂CMe ₂], trans-[PtCl₂(imine-a)(imine-b)] 12 [imine-b = NHC(CH₂CO₂Me)ONEt₂] or trans-[PtCl ₂(imine-a)(oxadiazoline-b)] 13. The cis mono-imine mixed ligand complex cis-[PtCl₂(imine-a)(NCCH₂CO₂Me)] 4a is the major product from the reaction of cis-[PtCl₂(NCCH ₂CO₂Me)₂] 1a with the oxime 2, while the di-imine compound cis-[PtCl₂(imine-a)₂] 5a is a minor product. Reaction of cis-[PtCl₂(imine-a)(NCCH₂CO ₂Me)] 4a with N,N-diethylhydroxylamine 11 or the cyclic nitrone 8 affords, in good yields, the unsymmetric mixed ligand complexes cis-[PtCl ₂(imine-a)(imine-b)] 12a or cis-[PtCl₂(imine-a) (oxadiazoline-b)] 13a, respectively. All these complexes were characterized by elemental analyses, IR and ¹H, ¹³C and ¹⁹⁵Pt NMR spectroscopies, and FAB⁺-MS. The X-ray structural analysis of trans-[PtCl₂{NHC(CH₂CO₂Me)ONCMe ₂}(NCCH₂CO₂Me)] 4 is also reported. The Royal Society of Chemistry.

Full text of DOI:10.1039/b704329e

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www.rsc.org/dalton | Dalton Transactions
Mixed unsymmetric oxadiazoline and/or imine platinum(II) complexes†‡§
Jamal Lasri,a M. Ad´ılia Janua´rio Charmier,*a,b M. Fa´tima C. Guedes da Silvaa,b and Armando J. L. Pombeiro*a
Received 21st March 2007, Accepted 4th May 2007
First published as an Advance Article on the web 1st June 2007
DOI: 10.1039/b704329e
=
Iminoacylation of acetone oxime Me2C NOH 2 upon reaction with trans-[PtCl2(NCCH2CO2Me)2] 1
−
+
=
and [2 + 3] cycloaddition of acyclic nitrone O N(Me) C(H)(C6H4Me-4) 3 to a nitrile ligand in 1 lead
=
to the formation of mono-imine trans-[PtCl2(imine-a)(NCCH2CO2Me)] 4 [imine-a = NH C-
=
(CH2CO2Me)ON CMe2] and mono-oxadiazoline trans-[PtCl2(oxadiazoline-a)(NCCH2CO2Me)] 6
=
[oxadiazoline-a = N C(CH2CO2Me)ON(Me)C(H)(C6H4Me-4)] unsymmetric mixed ligand complexes,
respectively, as the main products. Reactions of 6 or 4 with acetone oxime 2, cyclic nitrone
−
+
=
O N CHCH2CH2CMe2 8 or N,N-diethylhydroxylamine 11 give access, in moderate to good
yields, to the unsymmetric mixed ligand oxadiazoline and/or imine complexes trans-[PtCl2-
(oxadiazoline-a)(imine-a)] 9, trans-[PtCl2(oxadiazoline-a)(oxadiazoline-b)] 10 [oxadiazoline-b =
=
N C(CH2CO2Me)ONC(H)CH2CH2CMe2], trans-[PtCl2(imine-a)(imine-b)] 12 [imine-b =
=
NH C(CH2CO2Me)ONEt2] or trans-[PtCl2(imine-a)(oxadiazoline-b)] 13. The cis mono-imine mixed
ligand complex cis-[PtCl2(imine-a)(NCCH2CO2Me)] 4a is the major product from the reaction of
cis-[PtCl2(NCCH2CO2Me)2] 1a with the oxime 2, while the di-imine compound cis-[PtCl2(imine-a)2] 5a
is a minor product. Reaction of cis-[PtCl2(imine-a)(NCCH2CO2Me)] 4a with
N,N-diethylhydroxylamine 11 or the cyclic nitrone 8 affords, in good yields, the unsymmetric
mixed ligand complexes cis-[PtCl2(imine-a)(imine-b)] 12a or cis-[PtCl2(imine-a)(oxadiazoline-b)] 13a,
respectively. All these complexes were characterized by elemental analyses, IR and 1H, 13
and 195Pt NMR spectroscopies, and FAB+-MS. The X-ray structural analysis of
C
=
=
trans-[PtCl2{NH C(CH2CO2Me)ON CMe2}(NCCH2CO2Me)] 4 is also reported.
Compared to its common application, ligand exchange reac-
tions, much less use has been made of selective differentiation be-
tween initially equivalent ligands,8h,14,15,16 although such behaviour
has been observed in some cases, for example in the reactions of
cis- or trans-[PtCl2(NCPh)2] with the secondary aliphatic amines
RRꢀNH (R = Me; Rꢀ = Et, But) to produce the mono-amidine
Introduction
Apart from the relevance of platinum compounds with N-ligands
in pharmaceutical chemistry due to their antitumor activity,1,2 the
synthetic use of organonitrile–Pt complexes as precursors for a
wide variety of N-containing Pt compounds is also a matter of
current interest.3–7 It has been shown that, when coordinated to
a suitable PtII or PtIV center, nitrile ligands can undergo coupling
with different types of nucleophiles8,9 or 1,3-dipole reagents.10 For
instance, in our earlier work we have shown that nitriles of the type
NCCH2R (R = CO2Me, Cl) in [PtCl2(NCCH2R)2] compounds
undergo [2 + 3] cycloaddition with cyclic or acyclic nitrones
to afford di(oxadiazoline) complexes11,12 while iminoacylation
of ketoximes leads to the formation of di(imine)platinum(II)
complexes,13 under mild conditions. In such reactions, both ligated
nitriles were transformed into the derived ligands. The major
resulting achiral and symmetrical products were generally stable
and obtained as mixtures of 1 : 1 diastereoisomers, unsuitable for
application in asymmetric chemistry.
ꢀ
8h
=
complexes cis- or trans-[PtCl2{N(H) C(NRR )Ph}(NCPh)],
and in the [2 + 3] cycloaddition of nitrones to afford mono and
mixed oxadiazoline complexes.16 In this last case, a geometrical
dependence is observed, since the cis-mono(oxadiazoline)(nitrile)
complexes do not undergo further cycloaddition with a second
equivalent of acyclic nitrone, in contrast to the corresponding
trans-complexes.16
Aiming to contribute to the development of the synthesis of
unsymmetric mixed ligand PtII complexes, and to study some
electronic factors of their selectivity, we have now focused our
attention on the preparation of novel polyfunctional cis and
trans unsymmetric complexes, such as [PtCl2(oxadiazoline-a)-
(imine-a)], [PtCl2(oxadiazoline-a)(oxadiazoline-b)], [PtCl2(imine-
a)(oxadiazoline-b)] and [PtCl2(imine-a)(imine-b)], each bearing
two different ligands. Recently, it has been shown that a cis-
mono(oxadiazoline)(nitrile) complex does not react further with
an acyclic nitrone;16 we attempted the addition of a different 1,3-
dipolar reagent or nucleophile i.e. a cyclic nitrone or N,N-diethyl-
hydroxylamine to the nitrile group in a cis-mono(imine)(nitrile)
complex. Interestingly, cis-[PtCl2(imine-a)(nitrile)] is converted
to mixed ligand unsymmetric complexes cis-[PtCl2(imine-a)-
(oxadiazoline-b)] or cis-[PtCl2(imine-a)(imine-b)] by reaction with
a second equivalent of this reagent, giving the first examples of
aCentro de Qu´ımica Estrutural, Complexo I, Instituto Superior Te´cnico, TU
Lisbon, Av. Rovisco Pais, 1049-001, Lisboa, Portugal. E-mail: pombeiro@
ist.utl.pt
bUniversidade Luso´fona de Humanidades e Tecnologias, Av. Campo Grande
no 376, 1749-024, Lisboa, Portugal. E-mail: adilia.charmier@ist.utl.pt
† The HTML version of this article has been enhanced with colour images.
‡ CCDC reference number 641242. For crystallographic data in CIF or
other electronic format see DOI: 10.1039/b704329e
§ Electronic supplementary information (ESI) available: Crystallographic
details. See DOI: 10.1039/b704329e
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these types of compounds. This may eventually offer an interesting
application in the synthesis of biologically relevant molecules, and
further studies are in progress.
Results and discussion
In this study, we report the synthesis of new trans- and cis-mixed
unsymmetric oxadiazoline and/or imine complexes by using the
bis(methylcyanoacetate) complexes trans- and cis-[PtCl2(NCCH2-
CO2Me)2] as starting dinitrile PtII complexes, and acetone oxime
−
+
=
=
Me2C NOH 2, the acyclic nitrone O N(Me) C(H)(C6H4Me-4)
−
+
=
3, the cyclic nitrone O N CHCH2CH2CMe2 8 or N,N-diethyl-
hydroxylamine 11, as the reacting nucleophiles.
All the complexes obtained, whose formation was monitored by
TLC, were purified by column chromatography on silica gel and
characterized by IR, 1H, 13C and 195Pt NMR spectroscopy, FAB+-
MS and elemental analyses (in one case also by single-crystal X-ray
diffraction).
Reactions of trans-[PtCl2(NCCH2CO2Me)2] 1
Trans-[PtCl2(NCCH2CO2Me)2] 1 is fully soluble in CH2Cl2 and
thus the reactions of this complex with acetone oxime 2 and
the acyclic nitrone 3, the former leading to imine complexes via
iminoacylation of the oxime and the latter affording oxadiazoline
species upon [2 + 3] cycloaddition to a nitrile ligand, occur in
homogenous media with favourable 1 : 1 stoichiometric conditions.
The reactions were carried out in a 0.1 mmol scale with equimolar
amounts of trans-[PtCl2(NCCH2CO2Me)2] 1 and the nucleophile.
The iminoacylation of acetone oxime 2 proceeds under mild
conditions (40 ◦C, 15 min), in dry CH2Cl2, to give the mono-imine
Scheme 1 (The mixed ligands complexes 4 and 6 are the major products.)
(1657 cm−1) complexes. In the 1H NMR spectrum of 4, the
chemical shift of the NH proton is detected at 8.17 ppm, which
indicates the existence of a hydrogen bond between the imine
hydrogen and oxime nitrogen atoms which stabilizes the E-
conformation of the iminoacyl ligands. The 13C NMR spectrum of
4 shows the expected signals of the iminoester and nitrile ligands.
The single crystal X-ray diffraction structural analysis
=
trans-[PtCl2(imine-a)(NCCH2CO2Me)] 4 [imine-a = NH C-
=
(CH2CO2Me)ON CMe2] as the major product (51% yield),
of the mono-iminoacylated PtII complex trans-[PtCl2{NH C-
together with the known13 bis-imine trans-[PtCl2(imine-a)2] 5
(17%) (Scheme 1). In the case of the reaction of trans-[PtCl2-
(NCCH2CO2Me)2] 1 with the acyclic nitrone 3, the system was
stirred, in dry CH2Cl2, at 40 ◦C for 8 h to give the mono-
=
=
(CH2CO2Me)ON CMe2}(NCCH2CO2Me)] 4 confirms the for-
mulation and trans configuration (the molecular structure is
depicted in Fig. 1, crystal data and selected bond lengths and
angles are given in Tables 1 and 2, respectively). The values of
oxadiazoline trans-[PtCl2(oxadiazoline-a)(NCCH2CO2Me)]
6
˚
˚
bond lengths Pt–N(1) [1.991(4) A], Pt–N(2) [1.980(5) A], Pt–Cl(1)
=
[oxadiazoline-a = N C(CH2CO2Me)ON(Me)C(H)(C6H4Me-4)]
as the main product (52% yield), along with the known12 bis-
(oxadiazoline) trans-[PtCl2(oxadiazoline-a)2] 7 (25%) (Scheme 1).
The complexes 5 and 7 derived from nucleophilic additions
to both nitrile ligands are formed in much lower yields; thus
the reactions show a considerable selectivity towards the mixed
ligand products derived from a single addition, i.e. 4 and 6 (major
products).
˚
˚
˚
[2.293(14) A], Pt–Cl(2) [2.299(13) A], N(1)–C(10) [1.282(7) A],
˚
˚
N(2)–C(20) [1.128(7) A] and N(1)–H(1) [0.87(5) A], and angles
Once the first iminoacylation or cycloaddition has taken place,
the second nitrile ligand exhibits a lower reactivity due to the
different electronic properties of the imine or the oxadiazoline
now in the trans-position, in comparison with the nitrile in 1.
Steric effects are not expected to play an important role because
the ligands concerned are in trans positions.
Complexes 4 and 6 were derived from a single iminoacylation
or a single cycloaddition, respectively, and their IR spectra exhibit
quite similar m(N≡C) values (2338 or 2336 cm−1, respectively)
which are also identical to that of the starting material 1
−1
−1
=
Fig. 1 Molecular structure of the mono-iminoacylated PtII complex
(2337 cm ). The N C vibrations (1647 and 1666 cm for 4,
or 1660 cm−1 for 6) are also comparable with those of the corres-
ponding bis-imine 5 (1646 and 1666 cm−1) or bis-oxadiazoline 7
=
=
trans-[PtCl2{NH C(CH2CO2Me)ON CMe2}(NCCH2CO2Me)] 4 with
atomic numbering scheme (ellipsoids are drawn at 30% probability).
3260 | Dalton Trans., 2007, 3259–3266
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=
=
Table 1 Crystal data for trans-[PtCl2{NH C(CH2CO2Me)ON CMe2}-
(NCCH2CO2Me)] 4
4
Empirical formula
Fw
C11H17Cl2N3O5Pt
537.27
150(2)
0.71069
Orthorhombic
Pccn
15.1631(4)
29.3035(7)
7.5829(2)
90
Temp/K
˚
k/A
Cryst. syst.
Space group
˚
a/A
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
90
90
3
˚
V/A
3369.32(15)
8
2.118
8.670
18 444
Z
qcalc/mg m−3
l(Mo-Ka)/mm−1
No. of collected rflns
No. of unique rflns
RInt.
3069
0.0322
0.0283
0.0684
R1a (I ≥ 2r)
wR2b (I ≥ 2r)
Scheme 2
a R1 = RꢁFo|–|Fcꢁ/R|Fo|. b wR2 = [R[w(Fo2–Fc2)2]/R[w(Fo2)2]]1/2
.
1
In the H NMR spectrum of 10 the two expected signals of
the N–CH–N protons are detected at 5.88 (singlet) and 5.47
(multiplet) ppm, whereas in the 13C NMR spectrum, the N–CH–N
resonances appear at 92.5 and 90.0 ppm, assigned to the groups
at the oxadiazoline-a and oxadiazoline-b, respectively. The NMR
results show that complex 10 was isolated without undergoing ring
opening by N–O bond rupture of the oxadiazoline-b ligand. This
contrasts with what we have previously observed in the synthesis
of a symmetric bis(ketoimine) complex by reaction of 1 with
2 eq. of a cyclic nitrone (CH2Cl2, rt, 24 h);11 the formation of
the ketoimine compound is believed to proceed via an unstable
1,2,4-oxadiazoline complex which spontaneously rearranges to the
ketoimine product.11
◦
˚
Table 2 Selected bond lengths [A] and angles [ ] for 4
Pt(1)–Cl(1)
Pt(1)–N(1)
Pt(1)–N(2)
O(1)–C(10)
O(221)–(C22)
2.293(14)
1.991(4)
1.980(5)
1.330(7)
1.202(6)
O(1)–N(11)
N(2)–C(20)
N(1)–C(10)
N(1)–H(1)
1.457(6)
1.128(7)
1.282(7)
0.87(5)
O(222)–(C22)
1.314(6)
Cl(1)–Pt(1)–N(1)
Cl(2)–Pt(1)–N(2)
90.14(14) N(1)–Pt(1)–N(2)
91.05(14) N(11)–O(1)–C(10)
178.16(19)
111.6(4)
O(221)–C(22)–O(222) 125.4(5)
O(221)–C(22)–C(21) 123.6(5)
N(1)–H(1) · · · N(11) 114
Pt(1)–N(1)–H(1)
121(3)
Cl(1)–Pt(1)–N(1) [90.14(14)◦], Pt(1)–N(1)–H(1) [121(3)◦] and
Cl(1)–Pt(1)–N(2) [88.69(14)◦], as well as the N(1)–H(1) · · · N(11)
hydrogen bond between the imine hydrogen and oxime nitrogen
In order to obtain the desired mixed unsymmetric bis-
oxadioazoline complex 10 without undergoing ring opening by
N–O bond rupture, a close control of the time is required, i.e. the
reaction should not be allowed to proceed longer than 10 min.
The trans mono-imine complex [PtCl2(imine-a)(NCCH2CO2-
Me)] 4 is converted to the mixed unsymmetric complexes trans-
◦
˚
atoms [H(1) · · · N(11) is 2.14 A; N(1)–H(1) · · · N(11) is 114 ]
which stabilizes the E-conformation of the iminoacyl ligands,
agree with those reported for other bis-iminoacylated platinum(II)
complexes.8i,13
=
[PtCl2(imine-a)(imine-b)] 12 [imine-b = NH C(CH2CO2Me)-
1
The H and 13C NMR spectra of 6 show that the compound
ONEt2] (77% yield) or trans-[PtCl2(imine-a)(oxadiazoline-b)] 13
(81% yield) by reaction with a second equivalent of N,N-diethyl-
hydroxylamine 11 or cyclic nitrone 8, respectively (Scheme 3).
The IR spectra of these products do not exhibit any band
contains both an oxadiazoline and a nitrile ligand. In the 1H NMR
spectrum, the N–CH–N resonance is detected at 5.90 ppm, and,
in the 13C NMR spectrum, the N–CH–N resonance appears at
92.5 ppm, while the N≡C signal occurs at 112.8 ppm.
=
which can be assigned to m(N≡C), while m(N C) is observed in
the usual range. Both H and 13C NMR spectra of complex 12
1
The trans mono-oxadiazoline complex trans-[PtCl2(oxadiazo-
line-a)(NCCH2CO2Me)] 6 reacts with a second equivalent of
show that it contains two different iminoester ligands. The IR and
NMR data of complex 13 also prove that the compound can be
isolated without undergoing ring opening by N–O bond rupture
(see Experimental).
◦
−
+
=
acetone oxime 2 (40 C, 15 min) or cyclic nitrone O N CHCH2-
CH2CMe2 8 (rt, 10 min), in dry CH2Cl2, to form the new
mixed unsymmetric oxadiazoline-imine or bis-oxadiazoline
complexes trans-[PtCl2(oxadiazoline-a)(imine-a)] 9 (58% yield)
or trans-[PtCl2(oxadiazoline-a)(oxadiazoline-b)] 10 [oxadiazoline-
Reactions of cis-[PtCl2(NCCH2CO2Me)2] 1a
=
b = N C(CH2CO2Me)ONC(H)CH2CH2CMe2] (82% yield),
respectively (Scheme 2).
The complex cis-[PtCl2(NCCH2CO2Me)2] 1a was obtained by
replacement of the ligated EtCN in cis-[PtCl2(EtCN)2] by
NCCH2CO2Me under microwave irradiation (30 min, 110 ◦C).
The complex 1a has a lower solubility than its trans-isomer 1
Their IR spectra do not exhibit any band which can be assigned
−1
=
to m(N≡C), while m(N C) is observed at 1649 cm for 9 and
1660 cm−1 for 10.
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N≡CCH2CO2Me ligand in our complex 1a. Prolonged reflux
of the reaction mixture of the benzonitrile complex (40 ◦C,
10 d), in dry CH2Cl2, with an excess of cyclic nitrone or
N,N-diethylhydroxylamine, led to decomposition of the starting
material to form uncharacterised products.
Interestingly, the nitrile ligand in the cis mono-imine complex
4a can undergo further nucleophilic addition by reaction with a
second equivalent of N,N-diethylhydroxylamine 11 or cyclic ni-
trone 8, to give the mixed unsymmetric cis-[PtCl2(imine-a)(imine-
b)] 12a or cis-[PtCl2(imine-a)(oxadiazoline-b)] 13a complexes,
=
respectively (Scheme 5). The IR spectra show m(N C) in the range
1644–1666 cm−1 and do not exhibit any band corresponding to
m(N≡C).
Scheme 3
in common solvents, and therefore its reaction mixture with
=
the oxime Me2C NOH 2 is a suspension with an excess of the
latter reagent in solution. Nevertheless, the reaction affords the
monoacylated complex cis-[PtCl2(imine-a)(NCCH2CO2Me)] 4a as
the major product (50% yield), the diacylated compound cis-
[PtCl2(imine-a)2] 5a being formed only in 15% yield (Scheme 4).
Scheme 5
1
In the H NMR spectrum of 12a, the two distinct resonances
of the NH protons, detected at 8.20 and 8.55 ppm, are consistent
with the two hydrogen bonds (one for each imine ligand) between
the imine hydrogen and the oxime or the amine nitrogen atom,
which stabilize the E-conformation of the iminoacyl ligands.
Scheme 4 (The mixed ligand complex 4a is the major product.)
Concluding remarks
=
In the IR spectrum of compound 4a, m(N≡C) and m(N C) are
identical to the corresponding values of the parent complex 1a and
the cis bis-imine complex 5a, while the 13C NMR spectrum shows
the expected resonances. In the 195Pt NMR spectrum, the signals
of the cis-complexes 4a and 5a are shifted downfield with respect
to those of the trans-complexes 4 and 5. The shift is rather small
(Dd ∼ 16 ppm), as previously observed for other cis/trans-isomeric
PtII complexes.13,16,17
The results of this work show that a di(nitrile)-PtII complex of the
type trans- or cis-[PtCl2(NCR)2] (R = electron-acceptor group) can
act as a convenient starting material for the syntheses of a variety of
mixed ligand complexes formed upon sequential addition of protic
nucleophiles (such as an oxime or an hydroxylamine) and/or 1,3-
dipoles (an acyclic or a cyclic nitrone) (see the overall Scheme 6).
Thus, we can conclude that, in the mixed-ligand complexes
[PtCl2(imine-a)(NCR)] 4 or [PtCl2(oxadiazoline-a)(NCR)] 6, the
nitrile ligand is less reactive towards the nucleophile or the 1,3-
dipole than the nitrile ligands in the starting di(nitrile) complexes
which imparts selectivity to the process, the di(imine) or the
bis(oxadiazoline) complexes being formed in minor amounts. This
is suggestive of stronger electron-donor character in the imine and
oxadiazoline ligands in comparison with the nitrile, resulting in
the ligated nitrile in complexes 4 or 6 having a weaker activation
towards nucleophiles, than in the starting di(nitrile) complexes.
Recently, it was reported that the benzonitrile com-
plex cis-[PtCl2(oxadiazoline)(PhCN)] does not lead to cis-
[PtCl2(oxadiazoline)2] upon addition of a second equivalent of an
acyclic nitrone to the ligated PhCN.16 By repeating this experiment
with a second equivalent of the more reactive cyclic nitrone
8 or N,N-diethylhydroxylamine 11, we also observed that the
starting material was recovered quantitatively, conceivably due
to the weaker electrophilic character of the cyano-carbon of the
aromatic nitrile in comparison with that of the ester-substituted
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diethylhydroxylamine and acetone oxime were obtained from
commercial sources (Aldrich). C, H and N elemental analyses
were carried out by the Microanalytical Service of the Instituto
Superior Te´cnico. 1H, 13C and 195Pt NMR spectra (in CDCl3)
were measured on a Varian Unity 300 spectrometer at ambient
temperature. Positive-ion FAB mass spectra were obtained on a
Trio 2000 instrument by bombarding 3-nitrobenzyl alcohol (NBA)
matrices of samples with 8 keV (ca. 1.28 × 1015 J) Xe atoms. 1H,
13C chemical shifts (d) are expressed in ppm relative to Si(Me)4 and
195Pt chemical shifts are relative to Na2[PtCl6] (by using aqueous
K2[PtCl4], d = −1630 ppm, as a standard) with half-height line
width in parentheses. J values are in Hz. Infrared spectra (4000–
400 cm−1) were recorded on Bio-Rad FTS 3000MX and Jasco
FT/IR-430 instruments in KBr pellets and the wavenumbers
are given in cm−1. The microwave irradiation experiments were
undertaken in a focused microwave CEM Discover reactor (10 mL,
13 mm diameter, 300 W) which is fitted with a rotational system
and IR temperature detector.
Preparation of the organonitrile platinum(II) complex cis-
[PtCl2(NCCH2CO2Me)2] 1a by focused microwave irradiation.
Complex 1a was obtained by replacement of the ligated EtCN
in cis-[PtCl2(EtCN)2] by NCCH2CO2Me, under focused mi-
crowave irradiation. A solution of the ethanonitrile complex cis-
[PtCl2(EtCN)2] (40 mg, 0.10 mmol) in dry CH2Cl2 (1 mL) and
NCCH2CO2Me (2 mL) was added to a cylindrical Pyrex tube
which was then placed in a focused microwave reactor. After
reaction (110 ◦C, 30 min), the mixture was allowed to cool down.
The crude precipitated residue was filtered off, washed with diethyl
ether and dried in vacuo.
Scheme 6
Such behaviour results from a delicate balance of electronic
effects. For instance, when the organic group of the nitrile ligand
at PtII was an electron-donor (typically ethyl, in propionitrile),
the lower electrophilic character of the nitrile prevented it from
undergoing coupling with the oxime8i or the acyclic nitrone10e and
the PtII products of addition or [2 + 3] cycloaddition were obtained
indirectly, via reduction of the corresponding PtIV complexes.
The isolation of the mixed (imine)(nitrile) 4 or (oxadiazo-
line)(nitrile) 6 complexes allowed us to perform a further reaction,
in a controlled way, with a second equivalent of the protic
nucleophile or the 1,3-dipole (Scheme 6), providing easy and
selective access to mixed unsymmetric complexes which can
display heterocyclic ligands. As a final comment, the new mixed
unsymmetric cis- and trans-platinum(II) complexes which possess
an ester substituent are expected to be precursors for the synthesis
of amino acids and lactams,18 and eventually may also exhibit
anticancer activity (akin to other platinum complexes with N-
heterocyclic ligands);19 these applications are currently being
investigated by our group.
Yield: 80%. IR (cm−1): 2336 and 2339 (N≡C), 1738 (CO2Me).
FAB+-MS, m/z: 464 [M]+. The insolubility or instability of the
complex in normal solvents did not allow NMR spectra to be
obtained. Anal. Calcd for C8H10N2Cl2O4Pt: C, 20.70; H, 2.17; N,
6.04. Found: C, 20.95; H, 2.34; N, 6.16.
Reaction of trans-[PtCl2(NCCH2CO2Me)2] 1 or cis-[PtCl2-
=
(NCCH2CO2Me)2] 1a with Me2C NOH 2. A solution of 1 or
1a (50.0 mg, 0.107 mmol) in dry CH2Cl2 (3 mL) was added at
room temperature to the acetone oxime 2 (7.8 mg, 0.107 mmol)
and the mixture was heated with stirring at 40 ◦C for 15 min,
to form a bright yellow solution in the case of the trans isomer.
However, the cis isomer was less soluble and the reaction mixture
remained as a suspension. The progress of the reaction was
monitored by TLC. After evaporation of the solvent in vacuo to
dryness, the residue was washed with diethyl ether (5 × 3 mL
portions) and then purified by column chromatography (SiO2–
CH2Cl2, Et2O) followed by evaporation of the solvent in vacuo to
give the corresponding mono- and bis-iminoacylated products 4
and 5 or 4a and 5a, respectively.
Experimental
Materials and instrumentation
=
=
trans-[PtCl2{NH C(CH2CO2Me)ON CMe2 }(NCCH2CO2 -
Solvents were purchased from Aldrich and dried by usual proce-
dures. The complexes trans-[PtCl2(NCCH2CO2Me)2] 111 and cis-
[PtCl2(EtCN)2]20 were prepared according to published methods,
the latter by reaction of EtCN with aqueous tetrachloroplatinate
and subsequent chromatographic purification of the product.
The acyclic nitrone 3 was synthesized by condensation of 4-
methylbenzaldehyde and N-methylhydroxylamine, according to
the published method.21 Methyl cyanoacetate, cyclic nitrone, N,N-
Me)] 4. Yield: 51%. TLC on SiO2: Rf = 0.69 (eluent CH2Cl2–
Et2O (2 : 1)). IR (cm−1): 3496 (NH), 2338 (N≡C), 1748 (CO2Me),
1
=
1647 and 1666 (C N), 1179 (C–O). H NMR, d: 2.03 and 2.05
=
(two s, 3H each, CMe2), 3.79 and 3.86 (two s, 3H each, MeO),
3.90 and 4.18 (two s, 2H each, CH2), 8.17 (s, br, 1H, NH).
13C{ H} NMR, d: 18.1 and 22.4 (Me groups), 26.8 and 40.2 (CH2),
1
53.5 and 54.9 (MeO), 112.4 (N≡C), 161.8 and 166.6 (CO2Me),
167.0 ( CMe2), 168.8 (C(O) N). 195Pt NMR, d: −2250 (806 Hz).
=
=
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The Royal Society of Chemistry 2007
Dalton Trans., 2007, 3259–3266 | 3263
©

View Article Online
FAB+-MS, m/z: 537 [M]+. Anal. Calcd for C11H17N3Cl2O5Pt: C,
24.59; H, 3.19; N, 7.82. Found: C, 24.81; H, 3.04; N, 8.04.
=
Reaction of trans-[PtCl2{N C(CH2CO2Me)ON(Me)C(H)-
=
(C6H4Me-4)}(NCCH2CO2Me)] 6, trans-[PtCl2{NH C(CH2CO2-
=
=
Me)ON CMe2}(NCCH2CO2Me)] 4 or cis-[PtCl2{NH C(CH2-
=
=
trans-[PtCl2{NH C(CH2CO2Me)ON CMe2}2]
5. Yield:
=
CO2Me)ON CMe2}(NCCH2CO2Me)] 4a with acetone oxime 2
17%. TLC on SiO2: Rf = 0.55 (eluent CH2Cl2–Et2O (10 : 1)). All
the spectroscopic, FAB-MS and elemental analytical data are in
agreement with those reported previously.13
or N,N-diethylhydroxylamine 11. A solution of 6 (50.0 mg,
0.081 mmol), 4 or 4a (50.0 mg, 0.093 mmol) in dry CH2Cl2 (3 mL)
was added at room temperature to the acetone oxime 2 (1 eq.),
or N,N-diethylhydroxylamine 11 (1 eq.). The mixture was stirred
at 40 ◦C for 15 min and a bright yellow solution formed. The
progress of the reaction was monitored by TLC. After evaporation
of the solvent in vacuo to dryness, the residue was washed with
diethyl ether (5 × 3 mL portions) and then purified by column
chromatography (SiO2–CH2Cl2, Et2O) followed by evaporation of
the solvent in vacuo to give the final yellow powders of the 9, 12 or
12a products, respectively.
=
=
cis-[PtCl2{NH C(CH2CO2Me)ON CMe2}(NCCH2CO2Me)]
4a. Yield: 50%. TLC on SiO2: Rf = 0.58 (eluent CH2Cl2–Et2O
(2 : 1)). IR (cm−1): 3448 (NH), 2339 (N≡C), 1748 (CO2Me), 1647
1
=
and 1667 (C N), 1179 (C–O). H NMR, d: 2.04 and 2.06 (two s,
=
3H each, CMe2), 3.79 and 3.86 (two s, 3H each, MeO), 3.95 and
4.18 (two s, 2H each, CH2), 8.15 (s, br, 1H, NH). 13C{ H} NMR,
1
d: 18.0 and 22.4 (Me groups), 26.8 and 40.2 (CH2), 53.5 and 54.9
=
(MeO), 112.4 (N≡C), 161.9 and 166.6 (CO2Me), 167.0 ( CMe2),
168.7 (C(O) N). 195Pt NMR, d: −2234 (901 Hz). FAB+-MS, m/z:
=
537 [M]+. Anal. Calcd for C11H17N3Cl2O5Pt: C, 24.59; H, 3.19; N,
7.82. Found: C, 24.62; H, 3.04; N, 8.01.
=
trans-[PtCl2{N C(CH2CO2Me)ON(Me)C(H)(C6H4Me-4)}2 -
=
=
{NH C(CH2CO2Me)ON CMe2}] 9. Yield: 58%. TLC on
SiO2: Rf = 0.55 (eluent CH2Cl2–Et2O (20 : 1)). IR (cm−1): 3284
=
=
cis-[PtCl2{NH C(CH2CO2Me)ON CMe2}2]
5a. Yield:
1
=
(NH), 1749 (CO2Me), 1649 (C N), 1176 (C–O). H NMR, d:
15%. TLC on SiO2: Rf = 0.77 (eluent CH2Cl2–Et2O (2 : 1)).
=
1.99 and 2.01 (two s, 3H each, CMe2), 2.37 (s, 3H, CH3Ph),
−1
=
IR (cm ): 3436 (NH), 1746 (CO2Me), 1646 and 1667 (C N).
2.95 (s, 3H, CH3N), 3.74 and 3.85 (two s, 3H each, MeO), 3.97–
4.51 (m, 4H, CH2), 5.91 (s, 1H, N–CH–N), 7.24 (d, JHH 8.1 Hz,
2H, CHaromatic), 7.54 (d, JHH 8.1 Hz, 2H, CHaromatic), 8.05 (s, br, 1H,
1H NMR, d: 2.03 and 2.05 (two s, 3H each, CMe2), 3.80 (s,
=
3H, MeO), 4.20 (s, 2H, CH2), 8.18 (s, br, 1H, NH). 13C{ H}
1
NMR, d: 17.9 and 22.4 (Me groups), 40.0 (CH2), 53.4 (MeO),
NH). 13C{ H} NMR, d: 17.9 and 22.3 (Me groups), 22.0 (CH3Ph),
1
166.3 (CO2Me), 167.1 ( CMe2), 167.8 (C(O) N). 195Pt NMR, d:
−2064 (868 Hz). FAB+-MS, m/z: 611 [M + 1]+. Anal. Calcd for
C14H24N4Cl2O6Pt: C, 27.55; H, 3.96; N, 9.18. Found: C, 27.73; H,
4.02; N, 8.97.
=
=
34.0 (CH3N), 40.0 and 47.3 (CH2), 53.3 and 53.6 (MeO), 92.6
(N–CH–N), 128.4, 129.9, 133.6 and 139.9 (Caromatic), 164.4 and
166.2 (CO2Me), 166.4 ( CMe2), 166.9 and 167.8 (C(O) N). 195Pt
NMR, d: −2164 (806 Hz). FAB+-MS, m/z: 686 [M]+. Anal. Calcd
for C20H28N4O6Cl2Pt: C, 34.99; H, 4.11; N, 8.16. Found: C, 34.87;
H, 4.29; N, 8.28.
=
=
Reaction of trans-[PtCl2(NCCH2CO2Me)2] 1 with acyclic nitrone
−
+
=
O N(Me) C(H)(C6H4Me-4) 3. A solution of 1 (50.0 mg,
0.107 mmol) in dry CH2Cl2 (3 mL) was added at room temperature
to the acyclic nitrone 3 (15.9 mg, 0.107 mmol). The mixture
was heated with stirring at 40 ◦C for 8 h and a bright yellow
solution was formed. The progress of the reaction was monitored
by TLC. After evaporation of the solvent to dryness in vacuo, the
residue was purified by column chromatography (SiO2–CH2Cl2,
Et2O) followed by evaporation of the solvent in vacuo to give the
final yellow powders of the 6 and 7 products.
=
=
=
trans-[PtCl2{NH C(CH2CO2Me)ON CMe2 }{NH C(CH2 -
CO2Me)ONEt2}] 12. Yield: 77%. TLC on SiO2: Rf = 0.57 (eluent
CH2Cl2–Et2O (20 : 1)). IR (cm−1): 3213 (NH), 1747 (CO2Me), 1666
(C N), 1175 (C–O). H NMR, d: 1.10 (t, JHH 7.5 Hz, 3H each,
CH3CH2), 1.98 and 2.01 (two s, 3H each, CMe2), 2.92 (q, JHH
7.5 Hz, 2H each, CH3CH2), 3.75 and 3.76 (two s, 3H each, MeO),
1
=
=
4.06 and 4.15 (two s, 2H each, CH2), 8.16 and 8.5 (two s, br,
1
1H each, NH). 13C{ H} NMR, d: 12.2 (CH3CH2), 17.9 and 22.4
=
trans-[PtCl2{N C(CH2CO2Me)ON(Me)C(H)(C6H4Me-4)}-
(Me groups), 39.2 and 39.9 (CH2), 53.2 and 53.3 (MeO), 53.6
(NCCH2CO2Me)] 6. Yield: 52%. TLC on SiO2: Rf = 0.58 (eluent
=
(CH3CH2), 166.2 and 167.0 (CO2Me), 167.2 ( CMe2), 167.7 and
CH2Cl2–Et2O (10 : 1)). IR (cm−1): 3474 (NH), 2336 (N≡C), 1750
169.7 (C(O) N). 195Pt NMR, d: −2069 (806 Hz). FAB+-MS, m/z:
=
1
=
(CO2Me), 1660 (C N), 1176 (C–O). H NMR, d: 2.36 (s, 3H,
626 [M]+. Anal. Calcd for C15H28N4Cl2O6Pt: C, 28.76; H, 4.50; N,
8.94. Found: C, 28.81; H, 4.42; N, 8.87.
CH3Ph), 2.95 (s, 3H, CH3N), 3.81 and 3.83 (two s, 3H each, MeO),
3.88 (s, 2H, CH2), 3.98 (d, JHH 17.1 Hz, 1H, CH2), 4.44 (d, JHH
17.1 Hz, 1H, CH2), 5.90 (s, 1H, N–CH–N), 7.24 (d, JHH 7.8 Hz,
=
=
=
cis-[PtCl2{NH C(CH2CO2Me)ON CMe2}{NH C(CH2CO2-
2H, CHaromatic), 7.49 (d, JHH 7.8 Hz, 2H, CHaromatic). 13C{ H} NMR,
1
Me)ONEt2}] 12a. Yield: 70%. TLC on SiO2: Rf = 0.30 (eluent
d: 22.0 (CH3Ph), 26.7 (CH2), 34.2 (CH3N), 47.3 (CH2), 53.7 and
54.7 (MeO), 92.5 (N–CH–N), 112.8 (N≡C), 128.4, 130.1, 132.9
CH2Cl2–Et2O (20 : 1)). IR (cm−1): 3437 (NH), 1745 (CO2Me),
1
=
1665 and 1644 (C N), 1175 (C–O). H NMR, d: 1.15 (t, JHH
=
and 140.3 (Caromatic), 161.9 and 165.3 (CO2Me), 165.8 (C(O) N).
7.2 Hz, 3H each, CH3CH2), 2.02 and 2.05 (two s, 3H each,
195Pt NMR, d: −2329 (886 Hz). FAB+-MS, m/z: 613 [M]+. Anal.
Calcd for C17H21N3Cl2O5Pt: C, 33.29; H, 3.45; N, 6.85. Found: C,
33.24; H, 3.22; N, 6.76.
=
CMe2), 2.96 (q, JHH 7.2 Hz, 2H each, CH3CH2), 3.78 and 3.80
(two s, 3H each, MeO), 4.10 and 4.20 (two s, 2H each, CH2),
8.20 and 8.55 (two s, br, 1H each, NH). 13C{ H} NMR, d: 12.2
1
=
trans-[PtCl2{N C(CH2CO2Me)ON(Me)C(H)(C6H4Me-4)}2] 7.
(CH3CH2), 17.9 and 22.5 (Me groups), 39.3 and 40.0 (CH2), 53.3
=
(two diastereoisomers 1 : 1). Yield: 25%. TLC on SiO2: Rf = 0.64
(eluent CH2Cl2–Et2O (20 : 1)). All the spectroscopic, FAB-MS and
elemental analytical data are in agreement with those reported
previously.12
(MeO), 53.7 (CH3CH2), 166.2 (CO2Me), 167.2 ( CMe2), 167.8
and 169.6 (C(O) N). 195Pt NMR, d: −2052 (874 Hz). FAB+-MS,
=
m/z: 626 [M]+. Anal. Calcd for C15H28N4Cl2O6Pt: C, 28.76; H,
4.50; N, 8.94. Found: C, 28.91; H, 4.22; N, 8.75.
3264 | Dalton Trans., 2007, 3259–3266
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©

View Article Online
=
=
=
163.8 and 166.1 (CO2Me), 166.5 ( CMe2), 167.0 and 167.8
Reaction of trans-[PtCl2{NH C(CH2CO2Me)ON CMe2}-
(C(O) N). 195Pt NMR, d: −2151 (785 Hz). FAB+-MS, m/z: 650
=
=
=
(NCCH2CO2Me)]4,cis-[PtCl2{NH C(CH2CO2Me)ON CMe2}-
[M]+. Anal. Calcd for C17H28N4O6Cl2Pt: C, 31.39; H, 4.34; N, 8.61.
Found: C, 31.42; H, 4.03; N, 8.85.
=
(NCCH2CO2Me)] 4a or trans-[PtCl2{N C(CH2CO2Me)ON-
(Me)C(H)(C6H4Me-4)}(NCCH2CO2Me)] 6 with cyclic nitrone
−
+
=
O N CHCH2CH2CMe2 8. A solution of 4 or 4a (50.0 mg,
X-Ray crystallographic data for 4
0.093 mmol) or 6 (50.0 mg, 0.081 mmol) in dry CH2Cl2 (3 mL)
was added at room temperature to the cyclic nitrone 8 (1 eq).
The mixture was stirred at room temperature for 10 min and a
bright yellow solution formed. The progress of the reaction was
monitored by TLC. After evaporation of the solvent to dryness
in vacuo, the residue was purified by column chromatography
(SiO2–CH2Cl2, Et2O) followed by evaporation of the solvent
in vacuo to give the final yellow products 13, 13a or 10, respectively.
Intensity data were collected using a Bruker AXS-KAPPA APEX
II diffractometer using graphite monochromated Mo-Ka radia-
tion. Data was collected at 150 K using omega scans of 0.5◦ per
frame and a full sphere of data was obtained. Cell parameters were
retrieved using Bruker SMART software and refined using Bruker
SAINT on all the observed reflections. Absorption corrections
were applied using SADABS. Structure was solved by direct
methods by using the SHELXS-97 package22 and refined with
SHELXL-9723 with the WinGX graphical user interface.24 All
hydrogens were inserted in calculated positions except H1, H21A
and H21B which were located. Least square refinement with
anisotropic thermal motion parameters for all the non-hydrogen
atoms and isotropic for the remaining atoms gave R1 = 0.0283
[I > 2r (I); R1 = 0.0345 (all data)]. The maximum and minimum
peaks in the final difference electron density map are of 1.449 and
=
=
trans-PtCl2{N C(CH2CO2Me)ONC(H)(CH2CH2CMe2)} {N
C(CH2CO2Me)ON(Me)C(H)(C6H4Me-4)} 10. (two diastereoiso-
mers 1 : 1). Yield: 82%. TLC on SiO2: Rf = 0.50 (eluent CH2Cl2–
−1
=
Et2O (20 : 1)). IR (cm ): 1750 (CO2Me), 1660 (C N), 1171 (C–O).
1H NMR, d: 1.11 and 1.28 (two s, 3H each, Me), 1.58–1.77 (m,
2H, CH2), 2.18–2.25 (m, 1H, CH2), 2.38 (s, 3H, CH3Ph), 2.68–
2.73 (m, 1H, CH2), 2.96 (s, 3H, CH3N), 3.74 and 3.85 (two s, 3H
each, MeO), 3.79–4.04 (m, 3H, CH2CO2Me), 4.33–4.43 (m, 1H,
CH2CO2Me), 5.47 (m, 1H, N–CH–N, oxadiazoline-b), 5.88 (s, 1H,
N–CH-N, oxadiazoline-a), 7.25 (d, JHH 8.4 Hz, 2H, CHaromatic), 7.56
−3
˚
−1.452 e A , located around the platinum atom.‡
1
(d, JHH 8.4 Hz, 2H, CHaromatic). 13C{ H} NMR, d: 22.0 (CH3Ph),
Acknowledgements
23.3 and 27.6 (Me groups), 30.8, 30.9 and 34.0 (CH2), 34.2 (CH3N),
47.1 (CH2), 53.5 and 53.7 (MeO), 71.5 (Me2C-N), 90.0 (N–CH–
N, oxadiazoline-b), 92.5 (N–CH-N, oxadiazoline-a), 128.6, 129.9,
133.7 and 140.1 (Caromatic), 163.8 and 164.0 (CO2Me), 165.8 and
This work has been partially supported by the Fundac¸a˜o para
a Cieˆncia e a Tecnologia (FCT) and its POCI 2010 program
(FEDER funded) (Portugal). J. L. expresses gratitude to FCT
for a post-doc fellowship (grant SFRH/BPD/20927/2004).
166.1 (C(O) N). 195Pt NMR, d: −2247 (806 Hz). FAB+-MS, m/z:
=
726 [M]+. Anal. Calcd for C23H32N4O6Cl2Pt: C, 38.02; H, 4.44; N,
7.71. Found: C, 38.25; H, 4.51; N, 7.79.
References
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(b) Platinum-Based Drugs in Cancer Therapy, ed. L. R. Kelland and
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2 (a) G. Natile and L. G. Marzilli, Coord. Chem. Rev., 2006, 250, 1315;
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3 A. J. L. Pombeiro and V. Yu. Kukushkin, Reactivity of Coordinated
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Elsevier, Amsterdam, 2nd edn, 2003, vol. 1, ch. 1.34, pp. 639–660, and
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5 V. Yu. Kukushkin and A. J. L. Pombeiro, Coord. Chem. Rev., 1999, 181,
147.
=
trans-PtCl2{N C(CH2CO2 Me)ONC(H)(CH2 CH2 CMe2 )}
=
=
{NH C(CH2CO2Me)ON CMe2}] 13. Yield: 81%. TLC on
SiO2: Rf = 0.54 (eluent CH2Cl2–Et2O (10 : 1)). IR (cm−1): 1749
1
=
(CO2Me), 1657 and 1665 (C N), 1170 (C–O). H NMR, d: 1.13
and 1.31 (two s, 3H each, Me), 1.61–1.83 (m, 2H, CH2), 2.02 and
2.04 (two s, 3H each, CMe2), 2.28–2.36 (m, 1H, CH2), 2.89–
2.94 (m, 1H, CH2), 3.78 and 3.80 (two s, 3H each, MeO), 3.93 (d,
=
JHH 16.5 Hz, 1H, CH2), 4.12 (s, 2H, CH2), 4.25 (d, JHH 16.5 Hz,
1H, CH2), 5.56 (m, 1H, N–CH–N), 8.15 (s, br, 1H, NH). 13C{ H}
1
=
NMR, d: 17.9 and 22.4 ( CMe2), 23.4 and 27.6 (Me groups), 31.1,
34.1, 40.0 and 40.1 (CH2), 53.4 and 53.5 (MeO), 71.5 (Me2C-N),
=
90.2 (N–CH–N), 163.9 and 166.1 (CO2Me), 166.4 ( CMe2), 167.0
and 167.9 (C(O) N). 195Pt NMR, d: −2166 (765 Hz). FAB+-MS,
=
m/z: 650 [M]+. Anal. Calcd for C17H28N4O6Cl2Pt: C, 31.39; H,
6 R. A. Michelin, M. Mozzon and R. Bertani, Coord. Chem. Rev., 1996,
147, 299.
7 V. Yu. Kukushkin, D. Tudela and A. J. L. Pombeiro, Coord. Chem. Rev.,
1996, 156, 333.
4.34; N, 8.61. Found: C, 31.17; H, 4.23; N, 8.59.
=
=
cis-PtCl2{N C(CH2CO2Me)ONC(H)(CH2CH2CMe2)} {NH
8 (a) P. V. Gushchin, N. A. Bokach, K. V. Luzyanin, A. A. Nazarov, M.
Haukka and V. Yu. Kukushkin, Inorg. Chem., 2007, 46, 1684; (b) G. H.
Sarova, N. A. Bokach, A. A. Fedorov, M. N. Berberan-Santos, V. Yu.
Kukushkin, M. Haukka, J. J. R. Frau´sto da Silva and A. J. L. Pombeiro,
Dalton Trans., 2006, 3798; (c) A. V. Khripun, V. Yu. Kukushkin, S. I.
Selivanov, M. Haukka and A. J. L. Pombeiro, Inorg. Chem., 2006, 45,
5073; (d) K. V. Luzyanin, V. Yu. Kukushkin, M. L. Kuznetsov, A. D.
Ryabov, M. Galanski, M. Haukka, E. V. Tretyakov, V. I. Ovcharenko,
M. N. Kopylovich and A. J. L. Pombeiro, Inorg. Chem., 2006, 45,
2296; (e) V. Yu. Kukushkin and A. J. L. Pombeiro, Inorg. Chim. Acta,
2005, 358, 1; (f) A. Bokach, V. Yu. Kukushkin, M. Haukka, J. J. R.
Frau´sto da Silva and A. J. L. Pombeiro, Inorg. Chem., 2003, 42, 3602;
(g) A. V. Makarycheva-Mikhailova, N. A. Bokach, V. Yu. Kukushkin,
=
C(CH2CO2Me)ON CMe2}] 13a. Yield: 80%. TLC on SiO2:
Rf = 0.73 (eluent CH2Cl2–Et2O (5 : 1)). IR (cm−1): 1746 (CO2Me),
1
=
1647 and 1666 (C N). H NMR, d: 1.13 and 1.30 (two s, 3H
each, Me), 1.60–1.84 (m, 2H, CH2), 2.01 and 2.03 (two s, 3H each,
=
CMe2), 2.29–2.36 (m, 1H, CH2), 2.90–2.94 (m, 1H, CH2), 3.78
and 3.79 (two s, 3H each, MeO), 3.92 (d, JHH 17.1 Hz, 1H, CH2),
4.11 (s, 2H, CH2), 4.24 (d, JHH 17.1 Hz, 1H, CH2), 5.55 (m, 1H,
N–CH–N), 8.13 (s, br, 1H, NH). 13C{ H} NMR, d: 17.9 and 22.3
1
=
( CMe2), 23.3 and 27.5 (Me groups), 31.1, 34.2, 39.9 and 40.0
(CH2), 53.4 and 53.5 (MeO), 71.5 (Me2C-N), 90.0 (N–CH–N),
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The Royal Society of Chemistry 2007
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©

View Article Online
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